Your GP is likely to be breaking the law if s/he doesn't treat you because s/he thinks It's Just Your Age. The Equalities Act 2010 makes discrimination on the ground of age illegal. You can report the GP to the PCT or CCG in April or to the Equalities commission. You can also remind th GP that his Code of Practice - Good Medical Practice at paragraph 3b states that s/he must “take steps to alleviate pain and distress whether or not a cure may be possible”
the link is here